Eastern Bluebirds Alter their Song in Response to Anthropogenic Changes in the Acoustic Environment

Vocal responses to anthropogenic noise have been documented in several species of songbird. However, only a few studies have investigated whether these adjustments are made in real time or are longer-term responses to particular soundscapes. Furthermore, increased ambient noise often is accompanied by structural changes to the habitat, including the introduction of noisy roadways and the removal of native vegetation. To date, no studies have simultaneously investigated the impact of both acoustic and structural disturbance on the same species. The relevance of each of these variables must be quantified if we wish to refine our understanding of the ways in which human activities influence avian communication. In this study, we quantified both among-male and within-male adjustments of song in response to ambient noise, and also investigated whether anthropogenic modifications of the habitat explained variations in songs\u27 parameters. Recordings of songs were collected from male, breeding eastern bluebirds (Sialia sialis) residing in a network of nestboxes distributed across a gradient of anthropogenic disturbance. Levels of ambient noise were associated both with the average song-parameters of each male and with the change in a male\u27s song-parameters between the loudest and quietest periods at his nest box. Males\u27 song parameters were also related to habitat structure, as assessed using geographic information systems techniques. Males in noisier sites produced both higher-pitched and louder songs than did birds in quieter areas. Likewise, individual males demonstrated immediate adjustments to disturbance by noise, increasing the amplitude of their song between periods of quiet and loud ambient noise. Both spectral and temporal aspects of a male\u27s song were related to whether his habitat was more natural or anthropogenic. Our results indicate that males\u27 adjustments of song may represent simultaneous responses to multiple modifications of the habitat by humans. However, we also conclude that biotic noise remains an important influence on avian signals even in anthropogenic areas. We suggest that human habitats provide an ideal setting in which to perform experiments on communication strategies, with resulting data poised to reveal underlying evolutionary processes while also informing conservation and management

Acoustic Space is Affected by Anthropogenic Habitat Features: Implications for Avian Vocal Communication

Human-altered landscapes often include structural features, such as higher levels of impervious surface cover (ISC) and less vegetation, that are likely to affect the transmission of avian vocalizations. We investigated the relationships between human habitat modifications and signal transmission by measuring four acoustic parameters—persistence, reverberation, and signal-to-noise ratio (SNR) of broadcast tones, as well as absolute ambient noise level—in each of 39 avian breeding territories across an anthropogenic disturbance gradient. Using a geographic information system, we quantified the amounts of different habitat features (e.g., ISC, grass, trees) at each site; a principal component analysis was used to identify which of these habitat features commonly co-occurred (e.g., “habitat suites”). Finally, we used a model selection process to explore whether the habitat suites predicted the acoustic parameters. Tone persistence was higher and reverberation was lower in more open, grassy habitats than in areas with more vertical anthropogenic structures. In more human-modified sites, ambient noise levels were higher, leading to lower SNR. In habitats with low levels of human modification, we found that even small increases in the total amount of open—grassy area will quickly improve the acoustic space of singing birds. However, our results also indicated that there may be a critical level of human habitat modification above which the addition of “natural” areas does not benefit avian communication. Thus, we recommend that managers focus their efforts on preserving pre-existing “natural” habitat, rather than attempting to introduce it into areas that have already received significant human modification

Anthropogenic Noise is Associated with Reductions in the Productivity of Breeding Eastern Bluebirds (Sialia sialis)

Although previous studies have related variations in environmental noise levels with alterations in communication behaviors of birds, little work has investigated the potential long-term implications of living or breeding in noisy habitats. However, noise has the potential to reduce fitness, both directly (because it is a physiological stressor) and indirectly (by masking important vocalizations and/or leading to behavioral changes). Here, we quantified acoustic conditions in active breeding territories of male Eastern Bluebirds (Sialia sialis). Simultaneously, we measured four fitness indicators: cuckoldry rates, brood growth rate and condition, and number of fledglings produced (i.e., productivity). Increases in environmental noise tended to be associated with smaller brood sizes and were more strongly related to reductions in productivity. Although the mechanism responsible for these patterns is not yet clear, the breeding depression experienced by this otherwise disturbance-tolerant species indicates that anthropogenic noise may have damaging effects on individual fitness and, by extraction, the persistence of populations in noisy habitats. We suggest that managers might protect avian residents from potentially harmful noise by keeping acoustically dominant anthropogenic habitat features as far as possible from favored songbird breeding habitats, limiting noisy human activities, and/or altering habitat structure in order to minimize the propagation of noise pollution

Constraints on Acoustic Signaling Among Birds Breeding in Secondary Cavities: The Effects of Weather, Cavity Material, and Noise on Sound Propagation

Increasing evidence suggests that anthropogenic noise from urbanization affects animal acoustic communication. We investigated whether the begging calls of nestling Eastern Bluebirds (Sialia sialis) varied along a disturbance gradient of ambient noise. Contrary to our prediction and the results of a previous study of nestling Tree Swallows (Tachycineta bicolor), we found that nestling Eastern Bluebirds did not increase the amplitude or structural characteristics—including frequency, rate, and duration—of their vocalizations in response to ambient noise. However, we found that prevalent temperature and humidity conditions attenuated begging calls. Specifically, in warmer, more humid weather, vocalizations of nestling Eastern Bluebirds attenuated outside the nest box; this is consistent with research conducted on the propagation of sound in various mediums and temperatures. Finally, our results indicate that increased ambient noise is associated with a decrease in the signal-to-noise ratio of nestling vocalizations. In other words, loud ambient noise likely masks chick begging calls, which suggests that chicks and parents may experience communication difficulties in noisy environments. We suggest that future studies explore the effects of ambient noise on parental behavior and aspects of parent—offspring communication and conflict that are related to raising a brood of nestlings

Reproductive Success of Eastern Bluebirds (Siala sialis) on Suburban Golf Courses

Understanding the role of green space in urban—suburban landscapes is becoming critical for bird conservation because of rampant habitat loss and conversion. Although not natural habitat, golf courses could play a role in bird conservation if they support breeding populations of some native species, yet scientists remain skeptical. In 2003–2009, we measured reproduction of Eastern Bluebirds (Siala sialis) in Virginia on golf courses and surrounding reference habitats, of the type that would have been present had golf courses not been developed on these sites (e.g., recreational parks, cemeteries, agriculture land, and college campus). We monitored \u3e650 nest boxes and 2,255 nest attempts (n = 1,363 golf course, n = 892 reference site). We used an information-theoretic modeling approach to evaluate whether conditions on golf courses affected timing of breeding, investment, or nest productivity compared with nearby reference sites. We found that Eastern Bluebirds breeding on golf courses reproduced as well as those breeding in other disturbed habitats. Habitat type had no effect on initial reproductive investment, including date of clutch initiation or clutch size ( = 4 eggs). During incubation and hatching, eggs in nests on golf courses had higher hatching rates (80%) and brood sizes ( = 4.0 nestlings brood-1) than nests on reference sites (75% hatching rate; = 3.8 nestlings brood-1). Mortality of older nestlings was also lower on golf courses and, on average, golf course nests produced 0.3 more fledglings than nests on reference sites. Thus, within a matrix of human-dominated habitats, golf courses may support productive populations of some avian species that can tolerate moderate levels of disturbance, like Eastern Bluebirds

Effects of ambient noise on zebra finch vigilance and foraging efficiency.

Ambient noise can affect the availability of acoustic information to animals, altering both foraging and vigilance behaviour. Using captive zebra finches Taeniopygia guttata, we examined the effect of ambient broadband noise on foraging decisions. Birds were given a choice between foraging in a quiet area where conspecific calls could be heard or a noisy area where these calls would be masked. Birds foraging in noisy areas spent a significantly more time vigilant than those in quiet areas, resulting in less efficient foraging. Despite this there was no significant difference in the amount of time spent in the two noise regimes. However there did appear a preference for initially choosing quiet patches during individuals' second trial. These results emphasise how masking noise can influence the foraging and anti-predation behaviour of animals, which is particularly relevant as anthropogenic noise becomes increasingly prevalent in the natural world